This invention relates to a new and improved apparatus for grinding bulk specimens to remove surface irregularities and subsurface distortions. In particular, this invention relates to a new and improved grinding apparatus for use in the preparation of bulk metal specimens for electron-transmission microscopy.
The preparation of metal specimens for electron-transmission microscopy from bulk metal specimens ordinarily includes cutting thin slices from the bulk specimen, and grinding the slices to remove surface irregularities and subsurface distortions. The ground slices or platelets are subsequently thinned to electron transparency by chemical or electrolytic dissolution. The grinding process must be relatively gentle to minimize the depth of surface deformation and to avoid heating of the specimens. In addition, the grinding procedure should produce platelet specimens possessing substantially flat, parallel surfaces of uniform thicknesses of about 0.010 inch. These ground platelets facilitate the production of deformation-free foils by chemical or electrolytic dissolution. The production of satisfactory platelets by hand grinding is a slow process requiring considerable labor and care. Accordingly, automation of the grinding procedure has long been desired.
Grinding machines for automatic production of small flat specimens with controlled thickness are available commercially (e.g., Unipol PA-500, manufactured by Geos Corporation), but are relatively expensive, and generally do not provide the sometimes necessary option of grinding material from only one side of the specimen. Accordingly, the need for a relatively inexpensive and efficient means for producing substantially flat surface platelet specimens possessing uniform thickness still exists.
Another grinding apparatus identified as the 60-1908 AB Automet attachment and manufactured by Buchler, Ltd., has recently been used for fine grinding in metallography laboratories. In this apparatus, specimens in cylindrical mounts of standard diameter are clamped in a disk capable of holding several mounts. The mounted specimens are pressed against metallographic paper cemented on the flat, horizontal surface of a rotating grinding wheel. Adjustable spring pressure is applied at the center of the disk through a rotating shaft causing the disk to rotate during grinding providing equal average grinding conditions to all specimens. Initial efforts to utilize the 60-1908 AB Automet attachment for grinding platelets for electron transmission specimens did not produce platelets possessing the required flatness and uniform thickness. Accordingly, this device did not solve the problem of automatic production of platelet specimens possessing the flatness and uniform thickness required in electron-transmission microscopy. The present invention is directed to a new and improved grinding apparatus which automatically produces platelet specimens suitable for electron-transmission microscopy.